Impacto da atividade física e do tempo sedentário sobre a saúde cardiometabólica de adolescentes: uma substituição isotemporal de comportamentos

Abstract

This thesis aims to investigate the impacts of physical activity and sedentary behavior (SB) on the cardiometabolic health of male adolescents, using an isotemporal substitution approach. To achieve this general objective, two studies with specific objectives were conducted. The first study aimed to identify the daily behavioral pattern of these adolescents and to examine the theoretical effects of the isotemporal replacement of SB with light intensity physical activity (LIPA) or moderate to vigorous physical activity (MVPA) on cardiometabolic markers. The second study aimed to evaluate the effects of isotemporal replacement of sitting time (SIT) with standing time (STA) on the cardiometabolic biomarkers of these adolescents. This thesis was prepared with a convenience sample through cross-sectional studies and was composed of 92 male adolescents. Demographic, anthropometric, physiological, biochemical and accelerometric data were evaluated in both studies. In study 1, the adolescents' daily behavioral pattern was objectively measured for 7 consecutive days by the GT3X+ activity monitor. Activity counts by vector magnitude were used to estimate SB, LIPA and MVPA. Isotemporal substitution model was used to evaluate the effects of replacement of SB with LIPA or MVPA on cardiometabolic markers. In study 2, the SIT and daily STA of the adolescents were objectively assessed by the GT3X+ activity monitor for 7 consecutive days. MVPA was also estimated by a validated cutoff specific for young Brazilians. The effects of isotemporal replacement of SIT with STA on cardiometabolic biomarkers was verified. Covariance analysis (ANCOVA) with a Bonferroni post-hoc test was used to compare the adjusted averages between the four subgroups that were clustered according to the daily amount of SIT and STA. Adolescents (n = 84; age, 16.7 ± 0.9 years) wore the GT3X+ for 6.7 ± 0.6 days, during 15.2 ± 2.3 h, and spent 72.9% of the time in SB, 17.3% in LIPA, and 9.8% in MVPA. SB replacement with LIPA was associated with increased HDL-C, triglycerides (TG), HOMA2-IR, and HOMA2-S and decreased systolic blood pressure. In contrast, SB replacement with MVPA was associated with decreased in body fat percentage. Isotemporal substitution of SIT with STA was associated with total cholesterol (TC), non-HDL-C, LDL-C, and TG. ANCOVA results showed a statistically significant difference for TC, non-HDL-C, and LDL-C. These findings suggest that replacing SB with LIPA showed positive results on metabolic and physiological indicators, while replacing SB with MVPA was associated with only one obesity indicator. In addition, for male adolescents, sitting less and standing more may be an effective alternative to reduce cardiometabolic biomarker levels related to lipid metabolism, regardless of MVPA.